1. Field of the Invention
The present invention relates to an apparatus for preventing discharge of fuel vapor; and more particularly, to an apparatus for preventing such discharge from a vehicle fuel tank which is made to communicate with a charcoal canister via a vent tube at times when a fuel lid is opened by a fuel lid opener, for causing and fuel vapor to be adsorbed by the charcoal canister.
2. Description of the Related Art
A conventional apparatus for preventing discharge of fuel vapor from a vehicle fuel tank to the atmosphere when the fuel tank is being filled is disclosed in Japanese Patent Laid-Open No. 41244/1988.
This apparatus has a vent tube connecting the fuel tank to a charcoal canister for adsorbing fuel vapor. A solenoid valve which is disposed midway in the vent tube is normally closed when fuel lid is closed (locked state). A switch detects the actuation of the fuel lid opener and opens the solenoid valve.
Accordingly, at the time of refueling, if the locked fuel lid is operated to the unlocked state, an actuation detecting switch is turned on, which, in turn, causes the solenoid valve in the vent tube to open, thereby allowing fuel vapor in the fuel tank to flow into the charcoal canister via the vent tube for adsorption by the charcoal in the canister. As a result, it is possible to prevent the fuel vapor from being discharged via the inlet pipe (filler pipe) to the atmosphere during refueling.
This prior apparatus for preventing discharge of fuel vapor, uses an actuation detecting switch as shown in FIG. 13, wherein an actuation detecting switch 90 is disposed midway in a wire tube 92 covering a wire 94, which connects a lid opener lever to a fuel lid locking device. The opening and closing of actuation detecting switch 90 is controlled by an actuator 96 fixed to the movable wire 94.
Accordingly, after a fuel lid locking device is mounted to an automobile body, it is necessary to adjust the position of the wire tube 92 relative to the wire 94 so as to determine the relative position of the actuation detecting switch 90 and the actuator 96. This complicates the position adjusting operation, and decreases the efficiency assembly. In addition, even the fixing of a magnet to the wire and a lead switch to the wire tube does not make the adjusting operation any less complicated than the one described above.
In addition, since the actuator 96 is fixed to the wire 94, and the wire 94 is returned to its original position by the spring loaded automatic return of the lid opener lever, detecting switch or the lead switch is also opened, which in turn closes the solenoid valve. This causes a problem in that fuel vapor escapes through the inlet pipe during refueling. To solve this problem, Japanese Patent Laid-Open No. 53224/1987, proposed that the solenoid valve be held in the open state by a self-holding or stick circuit from the time that the fuel lid is opened until the vehicle is started. However, since the solenoid valve is electrically held open by the stick circuit, there is the possibility that the stick circuit may malfunction due to variations in voltage noise or the like, in which case the solenoid valve would close during refueling, causing the fuel vapor to be discharged to the atmosphere through the inlet pipe.
Of course, after refueling, it is necessary to close the solenoid valve to ensure that the fuel vapor will not escape from the fuel tank. However the above-described stick circuit device does not permit the solenoid valve to close unless the vehicle is started. Thus, if the vehicle is not started, the solenoid valve remains in the open state, permitting the fuel vapor in the fuel tank to flow into the charcoal canister after the lid is replaced on the inlet pipe of the tank.